Historically, the determinants of meal initiation and termination have been investigated with a primary focus on the momentary physiological state of the animal and the mechanisms that detect and respond to this state. A functional analysis suggests an alternative approach. Eating in meals and performing other activities in bouts makes possible the exploitation of resources (food, water, mates, nest sites, etc.) that are distributed discontinuously. Given a world of limited resources and the need to satisfy multiple requirements, each animal must efficiently allocate its time and effort among resources and activities or be outcompeted by individuals that do. Each activity involved in the use of a resource (discovery, selection, procurement, and consumption) is constrained by 1) the costs associated with that activity, 2) the animal's regulatory requirements for that resource, and 3) its requirements for other resources and activities. Natural selection has produced animals with behavioral and physiological mechanisms that are sensitive to these constraints; together, these permit the animal's many requirements to be satisfied efficiently. The behavioral mechanisms by which animals respond to these constraints are largely unknown, however, as is the manner in which behavioral and physiological mechanisms interact. Also not understood is how animals acquire and integrate the vast amount of information about potential resources, including their costs and benefits, that is necessary to regulate efficiently. Finally, the development of efficient behavioral strategies in young animals and the effect of conspecific competition on adults' strategies have only begun to be investigated. These are the problems that the proposed research seeks to address. To this end, we will use a foraging paradigm involving a naturalized laboratory setting in which freely-feeding animals can respond to various simulated constraints. Animals are housed 24 hours per day in an environment that offers food resources that differ in calorie content, taste, temporal patterns of availability and abundance, and the time and effort required to find, gain access to, and consume them. This paradigm allow the exploration of how, and in what form, animals acquire estimates of the current structure of their habitat while regulating intake effectively. Using this paradigm, we have already been highly successful in elucidating many of the rules of meal initiation, meal termination, and choice among food sources. The proposed research will extend our understanding of how regulation is achieved over the long term in the face of competing activities and fluctuating resources. Knowledge of the fundamental processes by which environmental and physiological factors interact to affect behavioral choice is prerequisite for a complete analysis of human feeding and regulation and their associated disorders.